Iran appears to have shut down part of its main export terminal of Kharg Island for repairs, according to oil industry sources, but it continues to export oil from other parts of the island at vastly reduced levels.

The level of Iran's oil exports has dropped from 1.9 million barrels a day earlier this summer to less than 1 million barrels a day, oil traders in the Gulf say. This is in part because of slack demand and partially because of efforts by the Organization of Petroleum Exporting Countries to stabilize the price of oil.

Iran's oil minister, Mohammed Gharazi, reportedly said late last month that Iran was only producing 1.2 million barrels of oil a day, half of its OPEC quota.

Whether this was a voluntary sacrifice or the result of marketing problems in a glutted market, Iran's production cut, along with Saudi Arabia's stated intention to produce just over 4 million barrels a day -- down from levels earlier this year of about 5 million barrels a day -- are policy moves that traders say have eased the strain on OPEC production ceilings.

Until Iran and Saudi Arabia cut back their production all OPEC producers were surpassing by over 1 million barrels a day a production ceiling of 17.5 million barrels a day set by the international organization in March 1983.

At least one section of the Kharg Island terminal, Sea Island, has been undergoing repairs since the end of June. But the sources said Iranian oil can still be exported from a jetty facility on the other side of the island.

The Sea Island facility was damaged in an Iraqi raid on the Greek tanker Alexander the Great that was berthed at Kharg on June 24.

The facility was capable of loading several 250,000-ton tankers at one time before it was damaged. Japanese oil sources in the Gulf estimate that the Iranians will maintain a "temporary closure" of the facility until the end of this month while repairs are made.

On the other side of the island the Iranians can take as many as six very large crude carriers, known as VLCCs, at a T-shaped jetty and sources here say that as far as they know traffic there has not been disrupted.

Shipping sources say the 250,000-ton tanker Rover Star left Kharg late last week. According to one Gulf industry source at least two tankers were berthed at Kharg more recently, the Gokturk scheduled to leave Kharg Sept. 2, and the M. Batan scheduled to leave Sept. 3., but these could not be confirmed independently.

Western oil industry sources based in the Gulf added that a complete closure of Kharg would almost cripple exploration and production in two large Iranian offshore fields that are serviced by supply and maintenance vessels based in Kharg. They said they were aware of no such disruption there.

Kharg Island has become a focal point of Iraqi threats leveled against Iran in its four-year-old war against that country.

Iraq has continually referred to its intention to maintain a "siege of Kharg Island" but this has been interpreted as referring to its missile attacks on tankers entering and leaving the oil terminal.

A full-scale attack on Kharg was thought by observers to be linked with the long-expected Iranian land offensive across the Iraqi border which the Iranians say has been delayed for tactical reasons. Military analysts continue to discount the feasibility of Iraqi planes mounting a successful strike against the terminal because of the island's heavily concentrated air defense systems.

Iran's only other offshore oil terminals, Lavan and Sirri, are in the southern gulf. Oil sources say that even though the islands could take two small tankers each at a time, the oil fields that feed the largest of the two, Lavan, can only supply 40,000 barrels per day and contracts for the oil have been committed at least until the end of the year.

Traders in the gulf say the drop in Iranian exports has less to do with problems at Kharg or Iraqi missile attacks than it has to do with Iranian pricing policies.

Ever since Iraqi missiles have been attacking Iranian supply vessels and tankers entering Iranian waters, the Japanese, one of Iran's principal customers have been negotiating with Iran for discounts on the price of Iranian oil to compensate for high war risk insurance premiums.

In the past the Japanese have been able to get as much as $2 or $3 slashed from the price per barrel but since the middle of August they have been running into a harder Iranian line.

Largely because the Iranians are unwilling to take more than 50 cents to $1 off of the price now, oil traders say, the Japanese are buying less Iranian oil.

They say the Japanese took 500,000 barrels per day in June and July but only 200,000 in August.

According to Japanese oil sources in the gulf, producers on both sides of the political fence are coming together to defend the $29 OPEC benchmark price. According to this theory, a number of recent Gulf moves are seen as resistance to pressures to lower the price.

Thus, Boeing Co. and Rolls Royce Ltd. and their Saudi customers are insisting publicly that a recent plane-for-oil barter deal will be conducted at the official OPEC price. The Iranians are holding fast against Japanese pleas for further discounts, and the Kuwaitis came up with an ingenious shuttle plan to deliver some oil to customers in their own tankers outside the Strait of Hormuz to weaken client pleas for price compensation against rising insurance premiums.